阅读说明：本技术 一种基于色差和谱域干涉的光学3d成像装置及方法 (Optical 3D imaging device and method based on chromatic aberration and spectral domain interference ) 是由 王毅 黄玉斌 马振鹤 赵玉倩 于 2021-08-30 设计创作，主要内容包括：本发明公开一种基于色差和谱域干涉的光学3D成像装置及方法,涉及光学干涉检测技术领域。该装置包括宽带光源,光源出射光入射第一透镜；第一透镜出射平行光入射分光装置；分光装置出射参考光和样品光；样品光依次经过第三透镜和第四透镜入射扫描振镜后经第五透镜以不同焦点聚焦在样品的不同深度层面上；参考光入射光栅,从光栅出射不同波长的参考光通过第二透镜聚焦反射镜表面；在第二透镜和反射镜之间设置三角形透光体；经反射镜反射的参考光和经样品的不同深度层面反射的样品光均进入分光装置后,再进入光谱仪中形成干涉光谱；光谱仪与扫描振镜均与计算机相连。实现了高纵向分辨率、高横向分辨率、大景深、大可测量角度,提高了解调精度。(The invention discloses an optical 3D imaging device and method based on chromatic aberration and spectral domain interference, and relates to the technical field of optical interference detection. The device comprises a broadband light source, wherein emergent light of the light source is incident to a first lens; the first lens emits parallel light to enter the light splitting device; the light splitting device emits reference light and sample light; sample light sequentially passes through a third lens and a fourth lens and then enters a scanning galvanometer and is focused on different depth layers of the sample through a fifth lens in different focuses; the reference light enters the grating, and the reference light with different wavelengths emitted from the grating passes through the second lens and focuses on the surface of the reflector; a triangular light-transmitting body is arranged between the second lens and the reflector; after the reference light reflected by the reflector and the sample light reflected by different depth layers of the sample enter the light splitting device, the reference light and the sample light enter the spectrometer to form an interference spectrum; the spectrometer and the scanning galvanometer are both connected with a computer. High longitudinal resolution, high transverse resolution, large depth of field and large measurable angle are realized, and the demodulation precision is improved.)

1. An optical 3D imaging device based on chromatic aberration and spectral domain interference is characterized by comprising a broadband light source, wherein emergent light of the broadband light source is incident to a first lens; the parallel light is emitted from the first lens and enters the light splitting device; emitting reference light and sample light from the light splitting device; the sample light enters a third lens, and the third lens emits sample light with different wavelengths; the sample light with different wavelengths is incident to the scanning galvanometer through the fourth lens and then is focused on different depth layers of the sample through the fifth lens at different focuses; the reference light incidence grating, the reference light of different wavelengths emitted from the grating is focused on the surface of the reflector through the second lens; a triangular light-transmitting body is arranged between the second lens and the reflector so as to change the optical paths of the reference lights with different wavelengths; reference light reflected by the surface of the reflecting mirror and sample light reflected by different depth layers of the sample enter the light splitting device and then enter the spectrometer to form an interference spectrum, and the spectrometer and the scanning galvanometer are connected with a computer.

2. The optical 3D imaging device based on chromatic aberration and spectral domain interference of claim 1, wherein the first lens is a collimating lens.

3. The optical 3D imaging device based on chromatic aberration and spectral domain interference of claim 1, wherein the third lens is a chromatic aberration lens.

4. The optical 3D imaging device based on chromatic aberration and spectral domain interference of claim 1, characterized in that the grating is a reflective grating.

5. The optical 3D imaging device based on chromatic aberration and spectral domain interference of claim 1, characterized in that the mirror is a plane mirror.

6. A method for optical 3D imaging based on chromatic aberration and spectral domain interference, the method comprising the steps of:

step 1: distributing emergent light of the broadband light source into reference light and sample light;

step 2: enabling the sample light to generate longitudinal dispersion through a chromatic aberration lens to obtain sample light with different wavelengths, enabling the sample light with different wavelengths to be respectively incident on a scanning galvanometer as parallel light, focusing light and diverging light, and enabling emergent light of the scanning galvanometer to be focused on different depth layers of the sample; meanwhile, the reference light is subjected to light splitting to obtain reference light with different wavelengths, and the reference light with different wavelengths is focused on the surface of the reflector in different optical paths;

and step 3: controlling the reference light reflected by the surface of the reflector and the sample light reflected by different depth layers of the sample to enter a spectrometer, forming an interference spectrum in the spectrometer and transmitting an interference spectrum signal to a computer;

and 4, step 4: transmitting a voltage signal through the computer to change the reflection angle of the X, Y galvanometer in the scanning galvanometer, so that the sample light is subjected to two-dimensional scanning at different depth levels of the sample, and correspondingly obtaining a corresponding interference spectrum signal on the computer;

and 5: carrying out high-pass filtering on the obtained interference spectrum signal in the computer, eliminating a direct current component and obtaining an alternating current component;

step 6: acquiring phase information of the alternating current component;

and 7: performing unwrapping processing on the phase of the alternating current component to obtain an unwrapped phase;

and 8: and performing first-order derivation on the unwrapped phase, and performing linear fitting on the result of the first-order derivation by using a least square method to obtain the upper and lower height difference of the sample surface corresponding to each measuring point, thereby realizing 3D imaging.

7. The method of optical 3D imaging based on chromatic aberration and spectral domain interference according to claim 6, characterized in that the method of distributing the outgoing light of a broadband light source into reference light and sample light is: the emergent light of the broadband light source is collimated and then distributed into reference light and sample light by the light splitting device.

8. The method of claim 6, wherein the method of obtaining phase information of the AC component is: and performing Hilbert transform on the alternating current component to obtain a sine term, and obtaining phase information of the alternating current component according to a trigonometric function relation.

Technical Field

The invention relates to the technical field of optical interference detection, in particular to an optical 3D imaging device and method based on chromatic aberration and spectral domain interference.

Background

With the development of precision manufacturing, the requirement for 3D imaging technology is higher and higher, and the optical interference technology is an important 3D imaging technology, has the advantages of non-contact and high resolution, and can achieve nanometer and sub-nanometer longitudinal resolution, but the longitudinal measurement range and the measurement angle of the optical interference technology are limited.

The longitudinal resolution, the transverse resolution and the measurement angle of 3D imaging are important factors for measuring the imaging technology, the longitudinal resolution is influenced by the interference technology, and the transverse resolution depends on the spot size of a light beam focused on a sample to be measured. In optical imaging techniques, the depth of field and the lateral resolution are a pair of mutually constrained parameters, the lateral resolution beingWhere λ is the wavelength, f is the focal length, d is the clear aperture of the lens, defined by the numerical aperture, NA-n sin α, where the aperture angle half α is smaller,it follows that if a high lateral resolution is desired, a large numerical aperture is used, but a large numerical aperture results in a reduced depth of field, i.e. a reduced longitudinal measurement range. In addition, since industrial detection exists in a large amount of transparent and highly reflective materials, such as mobile phone shells, glass panels, and finished metal surfaces, and the diffuse reflection of the surfaces of these materials is weak, and the specular reflection light enters the detection system mainly, as shown in fig. 1, the solid line represents the light cone irradiated to the sample, the dotted line represents the light cone specularly reflected by the surface of the sample, when the detection point angle is large, the reflected light cone deviates from a large direction, fig. 1 (a) represents the case that the numerical aperture is large, and the reflected light partially returns to the detection system, so that the interference spectrum can be measured, fig. 1 (b) represents the case that the numerical aperture is small, the reflected light cannot enter the detection system, the interference spectrum of the point cannot be measured, so that a large measurement angle requires a large numerical aperture, and a large numerical aperture is also beneficial for increasing the lateral resolution, but results in a smaller depth of fieldLimiting the longitudinal measurement range.

In optical 3D imaging, high lateral resolution, high longitudinal resolution, large depth of field and large measurable angular range are required, which are improved by increasing the numerical aperture, but at the same time the depth of field is also reduced. The chromatic aberration technology can solve the problem that the transverse resolution, the depth of field and the measurable angle range are mutually restricted, different focuses of multiple wavelengths can be formed by utilizing the dispersion principle, and the requirements of large depth of field, high transverse resolution and large measurement angle range can be simultaneously met. However, the chromatic aberration technique requires a light source with a large bandwidth, and for the same height, the frequency of the interference spectrum is proportional to the wave number bandwidth Δ k of the light source, which may result in a high frequency of the interference spectrum in optical 3D imaging, and when the frequency of the interference spectrum is high, the attenuation of the signal is large, which results in a low signal-to-noise ratio of the signal, and affects the demodulation accuracy.

Disclosure of Invention

In view of the above-mentioned deficiencies of the prior art, the present invention provides an optical 3D imaging apparatus and method based on chromatic aberration and spectral domain interference, which aims to solve the contradiction between lateral resolution, measurable angular range and large depth of field in optical 3D imaging.

The technical scheme of the invention is as follows:

the invention provides an optical 3D imaging device based on chromatic aberration and spectral domain interference, which comprises a broadband light source, a first lens and a second lens, wherein emergent light of the broadband light source is incident to the first lens; the parallel light is emitted from the first lens and enters the light splitting device; emitting reference light and sample light from the light splitting device; the sample light enters a third lens, and the third lens emits sample light with different wavelengths; the sample light with different wavelengths is incident to the scanning galvanometer through the fourth lens and then is focused on different depth layers of the sample through the fifth lens at different focuses; the reference light incidence grating, the reference light of different wavelengths emitted from the grating is focused on the surface of the reflector through the second lens; a triangular light-transmitting body is arranged between the second lens and the reflector so as to change the optical paths of the reference lights with different wavelengths; reference light reflected by the surface of the reflecting mirror and sample light reflected by different depth layers of the sample enter the light splitting device and then enter the spectrometer to form an interference spectrum, and the spectrometer and the scanning galvanometer are connected with a computer.

Further, according to the optical 3D imaging device based on chromatic aberration and spectral domain interference, the first lens is a collimating lens.

Further, according to the optical 3D imaging device based on chromatic aberration and spectral domain interference, the third lens is a chromatic aberration lens.

Further, according to the optical 3D imaging device based on chromatic aberration and spectral domain interference, the grating is a reflective grating.

Further, according to the optical 3D imaging device based on chromatic aberration and spectral domain interference, the mirror is a plane mirror.

The invention provides in a second aspect a method for optical 3D imaging based on chromatic aberration and spectral domain interference, the method comprising the steps of:

step 1: distributing emergent light of the broadband light source into reference light and sample light;

step 2: enabling the sample light to generate longitudinal dispersion through a chromatic aberration lens to obtain sample light with different wavelengths, enabling the sample light with different wavelengths to be respectively incident on a scanning galvanometer as parallel light, focusing light and diverging light, and enabling emergent light of the scanning galvanometer to be focused on different depth layers of the sample; meanwhile, the reference light is subjected to light splitting to obtain reference light with different wavelengths, and the reference light with different wavelengths is focused on the surface of the reflector in different optical paths;

and step 3: controlling the reference light reflected by the surface of the reflector and the sample light reflected by different depth layers of the sample to enter a spectrometer, forming an interference spectrum in the spectrometer and transmitting an interference spectrum signal to a computer;

and 4, step 4: transmitting a voltage signal through the computer to change the reflection angle of the X, Y galvanometer in the scanning galvanometer, so that the sample light is subjected to two-dimensional scanning at different depth levels of the sample, and correspondingly obtaining a corresponding interference spectrum signal on the computer;

and 5: carrying out high-pass filtering on the obtained interference spectrum signal in the computer, eliminating a direct current component and obtaining an alternating current component;

step 6: acquiring phase information of the alternating current component;

and 7: performing unwrapping processing on the phase of the alternating current component to obtain an unwrapped phase;

and 8: and performing first-order derivation on the unwrapped phase, and performing linear fitting on the result of the first-order derivation by using a least square method to obtain the upper and lower height difference of the sample surface corresponding to each measuring point, thereby realizing 3D imaging.

Further, according to the optical 3D imaging method based on chromatic aberration and spectral domain interference, the method of distributing the emergent light of the light source into the reference light and the sample light is: and after the emergent light of the light source is collimated, the emergent light is distributed into reference light and sample light by using a light splitting device.

Further, according to the optical 3D imaging method based on chromatic aberration and spectral domain interference, the method for acquiring the phase information of the alternating current component is: and performing Hilbert transform on the alternating current component to obtain a sine term, and obtaining phase information of the alternating current component according to a trigonometric function relation.

Generally, the above technical solution conceived by the present invention has the following beneficial effects compared with the prior art:

1. high longitudinal resolution is realized by using spectral domain interference, and high transverse resolution, large depth of field and large measurable angle are realized by using chromatic aberration.

2. The optical path of the reference arm is compensated according to the wavelength, and the interference spectrum frequency is reduced by combining the chromatic aberration effect, the attenuation of the signal is reduced, and the signal-to-noise ratio of the signal is improved, so that the demodulation precision is improved.

Drawings

FIG. 1 (a) is a schematic diagram showing the return of a portion of the reflected light to the detection system at a larger numerical aperture; (b) the figure shows a schematic diagram of the reflected light not entering the detection system when the numerical aperture is small;

FIG. 2 is a schematic structural diagram of an optical 3D imaging device based on chromatic aberration and spectral domain interference according to the embodiment;

FIG. 3 is a flow chart of the optical 3D imaging method based on chromatic aberration and spectral domain interference according to the present embodiment;

FIG. 4 is a schematic diagram showing the optical path of the sample light before reaching the sample surface according to the present embodiment;

FIG. 5(a) is a schematic view of a sample light measured with the reference arm closed; (b) a reference light indication diagram measured for closing the sample arm; (c) schematic interference spectra obtained for the open sample and reference arms simultaneously.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more clear, the present invention will be further described in detail with reference to the accompanying drawings and specific embodiments. The specific embodiments described herein are merely illustrative of the invention and are not intended to be limiting.

Fig. 2 is a schematic structural diagram of an optical 3D imaging device based on chromatic aberration and spectral domain interference according to the present embodiment, and as shown in fig. 2, the optical 3D imaging device based on chromatic aberration and spectral domain interference includes a broadband light source 1, and outgoing light of the broadband light source 1 is incident to a first lens 2; the parallel light emitted from the first lens 2 enters a light splitting device 3; emitting the reference light and the sample light from the spectroscopic device 3; the sample light sequentially passes through the third lens 4 and the fourth lens 5, is incident to the scanning galvanometer 16, and then passes through the fifth lens 8 to be focused on different depth layers of the sample 9 at different focuses; the reference light incidence grating 10, the reference light with different wavelengths emitted from the grating 10 is focused on the surface of a reflector 13 through a second lens 11; a triangular light-transmitting body 12 is arranged between the second lens 11 and the reflector 13 to change the optical path of the reference light with different wavelengths; reference light reflected by the reflecting mirror 13 and sample light reflected by different depth layers of the sample 9 enter the light splitting device 3 and then enter a spectrometer 14 to form an interference spectrum, and the spectrometer 14 and the scanning galvanometer 16 are both connected with a computer 15.

The first lens 2 is preferably a collimating lens; the light splitting device 3 is a device for splitting a beam of incident light into two beams of emergent light, such as a beam splitter, a beam splitter mirror and the like; the third lens 4 adopts a chromatic aberration lens, and the transverse resolution of the device can be improved by increasing the numerical aperture of the lens, so that the purpose is to generate a larger longitudinal measuring range and increase the measurable angle range of the sample. The fifth lens 8 is a focusing lens; the grating 10 adopts a reflective grating; the reflector 13 is preferably a plane reflector; the triangular light-transmitting body 12 is made of light-transmitting materials such as glass, resin, plastic and the like; the scanning galvanometer 16 consists of an X galvanometer 6 and a Y galvanometer 7, and the X galvanometer 6 and the Y galvanometer 7 are connected with the computer 15 simultaneously;

examples

The broadband light source 1 is connected with the collimating lens 2 through an optical fiber, and light emitted by the broadband light source 1 enters the collimating lens 2 through the optical fiber; the parallel light obtained after being collimated by the collimating lens 2 is incident on the beam splitter 3; the beam splitter 3 divides the incident light into two parts and distributes the two parts into two emergent lights of reference light and sample light; the reference light enters the reflective grating 10, is split by the grating 10 to obtain reference light with different wavelengths, and the reference light with different wavelengths emitted from the reflective grating 10 is focused on the surface of the plane mirror 13 through the convex lens 11; a triangular glass block 12 is arranged between the convex lens 11 and the plane mirror 13 to change the optical path of the reference light with different wavelengths; the sample light is incident to an X-vibration mirror 6 and a Y-vibration mirror 7 through a third lens 4 and a fourth lens 5 and then passes through a dispersion lens 8 to be focused on different depth layers of a sample 9 at different focuses; the process the reference light that plane mirror 13 reflects and the process the sample light that the different degree of depth aspect of sample 9 reflects gets into behind the beam splitter 3, reentrant spectrometer 14 form the interference spectrum in the spectrometer 14, and the spectrometer transmits spectral interference signal for computer 15, computer 15 still simultaneously with X shake the mirror 6 with Y shakes the mirror 7 and is connected.

In the imaging technology, the resolution is the center distance capable of resolving two points, the minimum center distance capable of just resolving is the highest resolution, and the smaller the visible resolution is, the better: from the longitudinal resolution formulaIt can be known that the adoption of a broadband light source increases the delta lambda and correspondingly decreases the delta z, so that the longitudinal resolution is improved; the lens numerical aperture defines the formula NA n sin alpha,it can be seen that the angle α can be increased by using a large numerical aperture, and the clear aperture d of the third lens (chromatic aberration lens) 4 is increased by the formula of the lateral resolutionAs can be seen, Δ x becomes smaller, thereby improving the lateral resolution; under the same numerical aperture, light reflected back to the lens generated by the inclination of the sample is inevitably lost, the larger the inclination angle is, the larger the loss is, if the inclination angle is not changed, the larger the numerical aperture of the lens is, the more the reflected back light is, the light loss is reduced, the inclinable angle range of the sample is increased to a certain extent, the measuring angle of the device is increased, and therefore better imaging is performed; by adopting a dispersion principle, focuses with different wavelengths are formed longitudinally, compared with the longitudinal focal shift generated by the original small-bandwidth wavelength, the longitudinal focal shift generated by the large-bandwidth wavelength is more obvious and wider, the method can be used for longitudinal large-range measurement, and the large depth of field is realized, as shown in figure 4, as the XY galvanometer only changes the direction of light and has no influence on final imaging, the XY galvanometer is omitted in figure 4 and is not drawn.

Fig. 3 is a flow chart of a method for optical 3D imaging based on chromatic aberration and spectral domain interference, as shown in fig. 3, the method comprising the steps of:

step 1: the emergent light of the light source is collimated and then distributed into reference light and sample light by a light splitting device;

in this embodiment, firstly, the light of the broadband light source 1 is collimated by the collimating lens 2, then the collimated light is incident into the beam splitter 3 in parallel, and is split by the beam splitter into two emergent lights of a sample light and a reference light;

step 2: enabling the sample light to generate longitudinal dispersion through a chromatic aberration lens to obtain sample light with different wavelengths, enabling the sample light with different wavelengths to be respectively incident on a scanning galvanometer as parallel light, focusing light and diverging light, and enabling emergent light of the scanning galvanometer to be focused on different depth layers of the sample; meanwhile, the reference light is subjected to light splitting to obtain reference light with different wavelengths, and the reference light with different wavelengths is focused on the surface of the reflector in different optical paths;

in this embodiment, after the sample light is longitudinally dispersed by the third lens 4, parallel light, focused light and divergent light with different wavelengths are incident on the scanning galvanometer through the fourth lens 5, and light emitted from the scanning lens is focused on different depth layers of the sample 9 through the fifth lens 8; meanwhile, the reference light is split by the grating 10 to obtain reference light with different wavelengths, the reference light with different wavelengths is focused on the surface of the reflector 13 through the second lens 11 and the triangular glass block 12, and the triangular glass block 12 is added between the second lens 11 and the reflector 13 and is used for changing the optical path of the reference light with different wavelengths, so that the function of compensating the optical path difference is achieved.

And step 3: controlling the reference light reflected by the surface of the reflector and the sample light reflected by different depth layers of the sample to enter a spectrometer, forming an interference spectrum in the spectrometer, and transmitting an interference spectrum signal to a computer by the spectrometer;

in this embodiment, the reference light reflected by the surface of the reflector 13 and the sample light reflected by different depth levels of the sample 9 form an interference spectrum in the spectrometer, and the spectrometer transmits an interference spectrum signal to the computer 15;

and 4, step 4: transmitting a voltage signal through the computer to change the reflection angle of the X, Y galvanometer in the scanning galvanometer, so that the sample light is subjected to two-dimensional scanning at different depth levels of the sample, and accordingly obtaining an interference spectrum signal shown in the formula (1) on the computer;

I(X,Y；K)＝α(X,Y；K)+β(X,Y；K)COS(K(H(X,Y)-aK-b)+φ) (1)

in the above formula, a and b are constants; due to the action of the triangular light-transmitting body 12, the optical paths of the reference light with different wavelengths are different, and aK + b is the optical path of the reference arm; x and Y represent the spatial coordinates of the scanning point; h (X, Y) represents relative height, namely the difference between the upper height and the lower height of the sample surface corresponding to the current measuring point; k represents the wave number coordinate of the spectrum collected by the spectrometer; since 3D imaging is a relative measurement, the constant b can be removed; phi represents the initial phase of the interference signal; alpha (X, Y; K) represents a direct current component; beta (X, Y; K) represents the intensity modulation function of the sample light due to chromatic aberration effects.

In the present embodiment, the scanning imaging process: to complete the imaging of an area, the computer 15 is required to control the X-galvanometer 6 and the Y-galvanometer 7 to realize two-dimensional scanning, that is, the reflection angles of the two galvanometers are changed by voltage signals transmitted by the computer, so as to change the position of the sample light focused on the sample surface, that is, the XY coordinates of the sample light on the sample surface are changed, and further, the interference spectrum I (X, Y; K) of each point on the sample surface is obtained by the spectrometer. In this embodiment, the sample light measured with the reference arm turned off is shown in fig. 5(a), the reference light measured with the sample arm turned off is shown in fig. 5(b), and the interference spectrum obtained with the sample arm and the reference arm turned on is shown in fig. 5 (c).

And 5: carrying out high-pass filtering on the interference spectrum signal shown in the formula (1), and eliminating a direct current component to obtain an alternating current component shown in the formula (2);

I₁(X,Y；K)＝β(X,Y；K)COS(K(H(X,Y)-aK-b)+φ) (2)

step 6: performing Hilbert transform on the alternating current component shown in the formula (2) to obtain a sine term shown in the formula (3), and obtaining phase information of the alternating current component shown in the formula (4) according to a trigonometric function relation;

I₂(X,Y；K)＝sin(K(H(X,Y)-aK-b)+φ) (3)

θ(X,Y；K)＝K(H(X,Y)-aK-b) (4)

and 7: performing unwrapping processing on the phase of the alternating current component obtained in the step 6 by using the existing demodulation technology to obtain an unwrapped phase;

since the operating range of the arctangent isStep 6 thereforeThe phase of the alternating current component is a winding phase, so that the existing demodulation technology is needed to be used for unwinding theta (X, Y; K), namely, the phase difference of adjacent points is judged, and when the phase difference is smaller than that of adjacent pointsPlus pi, the current difference is greater thanSubtracting pi to obtain a unwrapped phase θ 1(X, Y; K);

and 8: and performing first-order derivation on the unwrapped phase, and performing linear fitting on the result of the first-order derivation by using a least square method to obtain the upper and lower height difference of the sample surface corresponding to each measuring point, thereby realizing 3D imaging.

And performing first derivation on the unwrapped phase theta 1(X, Y; K) to obtain theta 2(X, Y; K) as H (X, Y) -2aK-b, performing linear fitting on the theta 2(X, Y; K) by using a least square method to obtain a and (H (X, Y) -b), wherein b can be ignored because the 3D imaging utilizes relative height imaging, and splicing the height information H (X, Y) to finally realize the 3D imaging.

If the optical path compensation of the reference light is not available, the frequency of the interference spectrum is H (X, Y), the signal frequency is high, the demodulation is not easy, the frequency of the interference spectrum can be (H (X, Y) -2aK-b) after the optical path of the reference arm is compensated according to the wavelength, and the chromatic aberration effect is combined, as shown in the formula (1), the frequency of the interference spectrum is reduced, the attenuation of the signal is reduced, the signal to noise ratio of the signal is improved, and therefore the demodulation precision is improved.

Finally, it should be noted that: the above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those skilled in the art; the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; such modifications and substitutions do not depart from the spirit and scope of the corresponding technical solutions as defined in the appended claims.